I really don't agree with that. Everything else you said was spot-on, but in my opinion the Obi-Wan we see in the OT flows naturally from that. I think that Obi-Wan was certainly not in denial in the OT about what happened to Anakin at all. "Vader was seduced by the dark side of the Force." That line couldn't have been clearer. Even in the original film, the young Vader was established as a pupil of Kenobi's who Kenobi had once thought was good. The quoted line indicates a fall from the good side to the bad side. As such it's an admission that Vader is now evil. If we accept that these lines are to be read with the understanding that they refer to Anakin, then implicitly they indicate an acceptance by Obi-Wan that Anakin has fallen into evil.